Cooling device, electronic apparatus, display unit, and method of producing cooling device

ABSTRACT

A cooling device includes a flow-path substrate, an intermediate substrate, and a lid-substrate each made of a polyimide resin, and a condenser substrate incorporated into holes of the intermediate substrate and an evaporator substrate which are made of a metal having a high thermal conductivity, whereby heat from a heat source can be enclosed into the evaporator substrate and the condenser substrate, so that the quantity of the latent heat can be substantially increased.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional application of U.S. Ser. No.10/608,153, filed Jun. 30, 2003.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a cooling device which is usedto reduce the temperature caused by heat generated, e.g., from a driverof a card type memory medium used in a personal computer, a digitalcamera, or the like, and to a method of producing the same. Moreover,the present invention relates to an electronic apparatus such as apersonal computer, a digital camera, or the like, on which the coolingdevice is mounted.

[0004] 2. Description of the Related Art

[0005] Storage media such as Memory Stick (registered trademark), SmartMedia (registered trademark), Compact Flash (registered trademark), andso forth are small in size and thickness, and also the storagecapacities can be considerably increased compared to conventionalstorage media such as Floppy (registered trademark) disks or the like.Thus, they have been generally used in electronic apparatuses such aspersonal computers, digital cameras, and so forth. Regarding some ofthese storage media, flash memories integrated with drivers are used, ordrivers are mounted on the main parts of apparatuses, other cards, orthe like. For the storage media, recently, the capacities have beensignificantly increased. With increasing of the storage capacities ofthe storage media as described above, problems have arisen in that muchheat is generated to cause defects in operation.

[0006] Accordingly, it has been proposed that a cooling device isprovided for a heat source in such an apparatus. For example, a coolingmethod using a heat pipe has been proposed.

[0007] A heat pipe is a metallic pipe of which the inner wall has acapillary structure, of which the inside is evacuated, and which tightlycontains a small amount of water or a substitution Freon therein. Whenone end of the heat pipe is brought into contact with a heat source tobe heated, the liquid contained therein is evaporated. Then, heat istaken into the gas as latent heat (evaporation heat). The heat istransferred to a low temperature region at a high speed (substantiallyequal to a sound velocity). The gas is cooled to be returned to theliquid, and the heat is released (the heat is released due to thecondensation latent heat). The liquid is passed through the capillarystructure (or due to the gravity) to be returned to its originalposition. Thus, the heat can be efficiently transferred.

[0008] However, the related art heat pipe is tubular and voluminous.Accordingly, the heat pipe is unsuitable as a cooling device for use inelectronic apparatuses such as personal computers, digital cameras, andso forth for which reduction of the size and the thickness is required.

[0009] Accordingly, to reduce the size of the heat pipe, a coolingdevice has been proposed in which grooves are formed on the surface of asilicon substrate and that of a glass substrate to be joined to eachother, and these substrates are joined to form the flow-path of a heatpipe between the substrates. When the joining is carried out, a smallamount of water or a substitution Freon is introduced to be tightlykept. The phase of the water or Freon is changed in the heat pipe, sothat the function of the heat pipe can be performed.

[0010] However, in the case in which the heat pipe is formed by use of asilicon substrate as described above, heat from an object to be cooledis diff-used, since the thermal conductivity of the silicon itself ishigh. Thus, there are problems in that the evaporation of a liquid inthe heat pipe is insufficient, or the evaporation is not caused at all,so that the function of the heat pipe can not be carried out.

[0011] Moreover, electronic apparatuses having silicone substratesmounted thereon have problems in that they may be broken in event thatthe apparatuses drop.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the present invention to providea cooling device of which the cooling performance, the thermalstability, and strength are superior, an electronic apparatus and adisplay unit each containing the cooling device, and a method ofproducing the cooling device.

[0013] According to a first aspect of the present invention, there isprovided a cooling device which comprises a first substrate havinggrooves constituting a heat pipe formed therein so as to be exposed tothe surface thereof, the grooves excluding at least the groovepositioned in correspondence to a wick, a second substrate made of ametal or a material having a thermal conductivity substantially equal tothat of a metal, the second substrate having at least the groove for thewick formed at the surface thereof, said surface being joined to thefirst substrate, and a third substrate into which the second substrateis incorporated so as to be exposed to the surface of the thirdsubstrate, said surface of the third substrate being joined to the firstsubstrate, at least one of the first substrate and the third substratebeing made of a polyimide resin.

[0014] According to the present invention, the second substrate having agroove for a wick formed on one side thereof is made of a materialhaving a thermal conductivity substantially equal to a metal. Thus, heatfrom a heat source can be efficiently transferred to the groove of thewick. On the other hand, the first substrate and so forth are made of apolyimide resin, so that the thermal conductivity is low. Thus, the heataccumulated in the wick is less diffused. Accordingly, the heat isenclosed in the wick, so that the quantity of the latent heat can besubstantially increased. Thus, the cooling performance of the heat pipecan be enhanced. In addition, the polyimide resin, which is thermallystable and flexible, is superior in strength. Thereby, the service lifeof the cooling device can be increased.

[0015] Preferably, the fourth substrate of the cooling device having atleast a groove for a condenser formed on the surface thereof is made ofa metal or a material having a thermal conductivity substantially equalto a metal. Thus, heat from a heat source can be efficiently transferredto the groove of the condenser. On the other hand, the first substrateand so forth are made of a polyimide resin, so that the thermalconductivity is low. Thus, the heat accumulated in the wick is lessdiffused. Accordingly, the heat is enclosed in the condenser, so thatthe quantity of the latent heat can be substantially increased. Thus,the cooling performance of the heat pipe can be enhanced.

[0016] Preferably, at least one of the second substrate and the fourthsubstrate is made of a metal containing copper or nickel. Therefore, theheat efficiency is enhanced.

[0017] Moreover, a thin film layer made of silicon or copper may beinterposed between the one side of the first substrate and the one sideof the third substrate. Thereby, the first substrate and the thirdsubstrate each made of a polyimide resin can be joined to each other viathe thin films of silicon or copper or via an adhesive provided betweenthe thin films. In this case, as the adhesive, a thermoplastic resinsuch as a thermoplastic polyimide or the like is suitably used.

[0018] Preferably, the first substrate and the third substrate joined toeach other are physically separated from each other into a regioncontaining the second substrate and a region containing the condenser asa component of the heat pipe, and the cooling device further comprises aflexible substrate interposed between the separated regions and has aflow-path formed therein so as to connect the wick and the condenser toeach other. This enables the flow-path substrate for forming a heat pipeto have a flexible shape.

[0019] According to a second aspect of the present invention, there isprovided a cooling device which comprises a first member having at leasta wick as a component of a heat pipe, a second member physicallyseparated from the first member and provided with a condenser as acomponent of the heat pipe, and a flexible substrate interposed betweenthe first member and the second member and having a flow-path forconnecting the wick and the condenser to each other formed therein, atleast one of the first member and the second member being made of apolyimide resin. Thus, the wick member and the condenser member can beinstalled, even if they are not arranged on a plane.

[0020] According to a third aspect of the present invention, there isprovided a cooling device which comprises: a first substrate having opengrooves constituting a heat pipe formed therein, the open grooveexcluding at least the open groove positioned in correspondence to awick; a second substrate made of a material having a thermalconductivity substantially equal to that of a metal, the secondsubstrate having at least the groove for the wick formed at the surfacethereof, said surface being joined to the first substrate; a thirdsubstrate into which the second substrate is incorporated so as toexposed to the surface of the third substrate, said surface of the thirdsubstrate being joined to the first substrate; and a lid-substratejoined to the surface of the first substrate so as to cover said surfacewhich is opposite to the side of the first substrate where the firstsubstrate and the second substrate are joined to each other; at leastone of the first substrate, the third substrate, and the lid-substratebeing made of a polyimide resin.

[0021] Thus, the lid-substrate is brought in close contact with the opengrooves of the first substrate, so that the flow-path of a heat pipe canbe formed, and the thickness of the first substrate becomes that of theflow-path. Thus, the flow-path is substantially increased in size, sothat the performance of the heat pipe is increased.

[0022] Preferably, the flow-path for a working fluid, formed by joiningof the open grooves of the first substrate and the lid-substrate, has adiamond-like carbon film formed on the inner wall thereof.

[0023] In the cooling device of the present invention, at least one ofthe first substrate, the third substrate and the lid-substrate is madeof a polyimide resin. The polyimide resin is water-absorptive to somedegree. Accordingly, in the case in which the flow-path for a workingfluid is made of a polyimide resin, the durability can be increased byformation of such a diamond-like carbon film on the surface of theflow-path.

[0024] According to a fourth aspect of the present invention, there isprovided an electronic apparatus which comprises: a slot to or fromwhich a card type storage device containing a flash memory and a drivercan be attached or detached; and a cooling device arranged adjacently tothe slot, the cooling device comprising a first substrate having groovesconstituting a heat pipe formed therein so as to be exposed to thesurface thereof, the groove excluding at least the groove positioned incorrespondence to a wick, a second substrate made of a metal or amaterial having a thermal conductivity substantially equal to that of ametal, the second substrate having at least the groove for the wickformed at the surface thereof, said surface being joined to the firstsubstrate, and a third substrate into which the second substrate isincorporated so as to be exposed to the surface of the third substrate,said surface of the third substrate being joined to the first substrate,the first substrate and the third substrate being made of a polyimideresin.

[0025] The present invention may be applied as cooling devices forcentral processing units of note-sizes personal computers, slots forattachment of external storage units, and drivers for liquid crystaldisplay units and so forth. Thereby, the cooling performance of theseapparatuses can be enhanced, and moreover, the apparatus can be given ahigh strength.

[0026] According to a fifth aspect of the present invention, there isprovided a method of producing a cooling device which comprises thesteps of a method of processing a cooling device comprising the steps offorming a first substrate made of a polyimide resin and having groovesconstituting a heat pipe formed therein so as to be exposed to thesurface thereof, the grooves excluding at least the groove positioned incorrespondence to a wick; forming a second substrate made of a metal ora material having a thermal conductivity substantially equal to that ofa metal, the second substrate having at least the groove for the wickformed on the surface thereof, incorporating the second substrate into athird substrate so as to be exposed to the surface of the thirdsubstrate, and joining the surface of the first substrate to the surfaceof the third substrate to each other. According to this invention, thecooling device having the above-described structure can be producedefficiently and securely.

[0027] Preferably, the method further comprises a step of incorporatingthe fourth substrate made of a metal or a material having a thermalconductivity substantially equal to that of a metal into the thirdsubstrate so as to be exposed to the surface of the third substrate.According to this structure, the condenser section is made of a materialhaving a high thermal conductivity, and thereby, heat can be effectivelytransferred.

[0028] The surface of the first substrate and that of the thirdsubstrate may be melt-joined to each other by heating the first andsecond substrates. Accordingly, the joining can be securely carried out,and the cost reduction becomes possible, due to the simple joiningprocess.

[0029] Preferably, the method further comprises a step of forming adiamond-like carbon film in the grooves of first substrate. Thus, theservice life of the substrate made of a polyimide resin is enhanced. Thecooling performance is enhanced, due to the increased fluidity of theworking fluid.

[0030] According to a sixth aspect of the present invention, there isprovided a method of producing a cooling device which comprises thesteps of forming a first substrate having open grooves constituting aheat pipe formed therein, the open grooves excluding at least the opengroove positioned in correspondence to a wick, forming a secondsubstrate made of a metal or a material having a thermal conductivitysubstantially equal to that of a metal, the second substrate having atleast the groove for the wick formed on the surface thereof, joining afirst surface of the first substrate to a lid-substrate to form aflow-path for a working liquid, incorporating the second substrate intoa third substrate so as to be exposed to the surface of the thirdsubstrate, and joining the surface of the third substrate to the secondsurface of the first substrate.

[0031] Thereby, the cooling device having the above-described structurecan be produced efficiently and securely.

[0032] Preferably, the method further comprises the steps of: forming afourth substrate made of a metal or a material having a thermalconductivity substantially equal to that of a metal, the fourthsubstrate having at least a groove for a condenser formed on the surfacethereof, and incorporating the fourth substrate intio the thirdsubstrate so as to be exposed to the surface of the third surface.Thereby, the heat-radiating means (condenser) can be efficientlyincorporated in the device.

[0033] Preferably, the step of forming the flow-path for a working fluidincludes a step of forming a diamond-like film on the surface of theflow-path. Thereby, the cooling device of which the substrates haveenhanced durability and cooling performance is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is an exploded perspective view showing the structure of acooling device according to the present invention;

[0035]FIG. 2 is a cross-sectional view of the assembled cooling deviceaccording to the embodiment of the present invention;

[0036]FIG. 3 consists of plan views of the respective substrates of thecooling device according to the embodiment of the present invention;

[0037]FIG. 4 is a plan view of the cooling device according to theembodiment of the present invention which is assembled by the flow-pathsubstrate, the intermediate substrate, the condenser substrate, and theevaporator substrate;

[0038]FIG. 5A is a perspective view of a silicon substrate;

[0039]FIG. 5B is a perspective view of a resin substrate;

[0040]FIG. 5C is a perspective view of a polyimide resin—metal compositesubstrate according to the present invention which is compared to thesilicon substrate of FIG. 5A and the polyimide resin substrate of FIG.5B from the standpoint of the thermal diffusion properties;

[0041]FIG. 6 illustrates a process of producing the cooling device ofthe present invention;

[0042]FIGS. 7A, 7B, 7C, 7D, and 7E schematically show a process offorming a flow-path substrate for use in the cooling device of thepresent invention;

[0043]FIGS. 8A, 8B, 8C, and 8D schematically show a process of forming acondenser substrate and an evaporator substrate for use in the coolingdevice of the present invention;

[0044]FIG. 9 schematically shows a process of joining the flow-pathsubstrate and a lid-substrate to each other which are used in thecooling device of the present invention;

[0045]FIG. 10 schematically shows a process of incorporating thecondenser substrate and the evaporator substrate into an intermediatesubstrate for use in the cooling device of the present invention;

[0046]FIG. 11 schematically shows a process of joining the flow-pathsubstrate and the intermediate substrate to each other, the flow-pathsubstrate having the lid-substrate joined thereto, the intermediatesubstrate having the condenser substrate and the evaporator substratejoined thereto;

[0047]FIG. 12 schematically shows a cooling device according to anotherembodiment of the present invention;

[0048]FIG. 13 is a schematic perspective view of a personal computer onwhich the cooling device of the present invention is mounted; and

[0049]FIG. 14 is a schematic perspective view of a liquid crystaldisplay unit on which the cooling device of the present invention ismounted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] Hereinafter, embodiments of the present invention will bedescribed with reference to the drawings.

[0051] (Cooling Device)

[0052]FIG. 1 is a perspective view of a cooling device according to thepresent invention which is in the dissembled state. FIG. 2 is across-sectional view of the cooling device which is in the assembledstate.

[0053] As shown in FIGS. 1 and 2, a cooling device 1 comprises fivesubstrates 10, 20, 30, 40, and 50. The flow-path substrate 10, theintermediate substrate 30, and the lid-substrate 50 are rectangular andare made of a polyimide resin which is not thermoplastic. The condensersubstrate 20 and the evaporator substrate 40 are rectangular substrates,e.g., made of a metal with a high thermal conductivity such as copper orthe like. The condenser substrate 20 and the evaporator substrate 40 areincorporated into holes 31 and 32 of the intermediate substrate 30,respectively. Regarding these five substrates 10, 20, 30, 40, and 50,the joining surfaces thereof are covered with a copper thin film (notshown in the drawings), respectively. These substrates are secured toeach other by hot-press joining via an adhesive layer 60 of athermoplastic polyimide resin (e.g., Upilex Vt., manufactured by UbeIndustries Ltd., etc.). Grooves 21 are formed on the surface 20 a of thecondenser substrate 20, and grooves 41 are formed on the surface 40 a ofthe evaporator substrate 40. An open groove 11 is formed in theflow-path substrate 10. Moreover, holes 31 and 32 are formed in theintermediate substrate 30. The grooves 21 and 41, the open groove 11,and the holes 31 and 32 are formed by bonding so as to function as aloop-shaped heat pipe.

[0054] Hereinafter, the constitution of the grooves 21 formed in thecondenser substrate 20, the grooves 41 formed in the evaporatorsubstrate 40, the open groove 11 in the flow-path substrate 10, and theholes 31 and 32 in the intermediate substrate 30, and the lid-substrate50 will be described with reference to FIG. 3.

[0055] As shown in FIG. 3, a copper thin-film (not shown) is formed onthe surface of the lid substrate 50 which is to be bonded to theflow-path substrate 10.

[0056] The open grooves 11 are formed in the flow-path substrate 10 soas to pass through the flow-path substrate 10, respectively. The opengrooves 11, when they are bonded to the lid-substrate 50 via theadhesion layer 60, form a liquid phase path 12 through which the liquidflows as a working fluid, a gas phase path 15 through which the gasflows as the working fluid, and a reservoir 13 in which the liquid isstored and supplied. Thin-films (not shown) of diamond-like carbon(hereinafter, referred to as DLC) may be formed in the liquid phase path12, the gas phase path 15, and the groove of the reservoir 13, which areformed by using the lid-substrate 50 and the flow-path substrate 10. Thepolyimide resin, which is a material for the lid-substrate 50 and theflow-path substrate 10, is water-absorptive to some degree. Thus,problematically, the substrate 50 and 10 may be distorted. The thin-filmlayers made of DLC function as protecting films, and thereby, thecooling device 1 has a superior durability.

[0057] The holes 31 and 32 are formed in the intermediate substrate 30so as to pass through the intermediate substrate 30.

[0058] The grooves 21 are formed on the surface 20 a of the condensersubstrate 20. The grooves 21 function as a condenser which condenses thegas introduced therein through the gas phase path 15 into the liquid,and circulates the produced liquid to a low temperature portion 16.

[0059] The grooves 41 are formed on the surface 40 a of the evaporatorsubstrate 40. The grooves 41 function as a cooling portion. The grooves41 function so that the liquid introduced through the liquid phase path12 or the reservoir 13 into the groves 41 is evaporated, and theproduced gas is flown into an evaporation portion 14.

[0060]FIG. 4 shows the substrates 10, 20, 30, 40, and 50 which arejoined to each other.

[0061] A liquid is placed and kept tightly inside of the heat pipe whichis formed by joining the substrate 10, 20, 30, 40, and 50. The liquidtightly enclosed in the heat pipe is circulated while it is changed fromits gas phase to its liquid phase, and vice versa in the heat pipe,whereby heat transfer is carried out. Thus, the cooling device 1functions.

[0062] Hereinafter, the circulation of the liquid and the gas isdescribed, in which the circulation starts at the liquid phase path 12for convenience' sake.

[0063] First, the liquid is flown into the evaporation portion 14through the liquid phase path 12. In this case, if the quantity of theliquid flown into the evaporation portion 14 is smaller than apredetermined amount, a liquid in such an amount as compensates for thedeficiency is supplied from the reservoir 13 so that the drying out isprevented.

[0064] The liquid flown into the evaporation portion 14 is heated toboil. The gas, which is produced by the boiling, is flown into the lowtemperature portion 16 via the gas phase path 15, and is condensed intothe liquid. The liquid, produced by the condensation, is flown from thelow temperature portion 16 into the liquid phase path 12 to becirculated.

[0065] According to this embodiment, the condenser substrate 20 and theevaporator substrate 40 are made of copper. However, as the materialsfor the substrates 20 and 40, silicon, nickel, or the like may be used.

[0066]FIGS. 5A, 5B, and 5C schematically show the areas where heat isdiffused on substrates in a predetermined time, respectively. FIG. 5Ashows the diffusion of heat on a silicon substrate. FIG. 5B shows thaton a polyimide resin substrate. FIG. 5C shows that on a compositesubstrate comprising a polyimide resin and a metal, such as copperincorporated into a polyimide resin substrate.

[0067] As shown in FIG. 5A, heat from a heat source A-1 for the siliconsubstrate is diffused in a wide area as shown by arrows (A-2) in FIG.5A. On the other hand, as shown in FIG. 5B, heat from a heat source B-1for the polyimide substrate is not widely diffused in a wide area asshown by the arrows in FIG. 5B (the heat is diffused in a region B-2).

[0068] A predetermined quantity or more of heat is required to beconcentrated to the evaporator so that the heat pipe can function. Inthe case in which the substrate is made of a silicon material as shownin FIG. 5A, the function of the heat pipe can not be sufficientlycarried out, since heat is excessively diffused.

[0069] Furthermore, the evaporator is required to have a thermalconductivity of a predetermined value or higher, so that the heat pipecan function. As shown in FIG. 5B, the thermal conductivity of thesubstrate made of a polyimide resin only is substantially zero, thefunction of the heat pipe can not be sufficiently carried out.

[0070] On the other hand, according to the present invention, as shownin FIG. 5C, heat from the heat source C-1 in the polyimide resin—metalcomposite substrate is highly diffused in the metal portion, and ishardly diffused in the polyimide resin region in the periphery of themetal portion (C-2). Thus, the heat is sufficiently transferred in theevaporator, while the heat is difficult to be diffused in thesurrounding polyimide resin portion. Therefore, the heat is concentratedto the evaporator. Thus, the function of the heat pipe can besatisfactorily carried out.

[0071] The cooling device 1 of the present invention comprises theflow-path substrate 10, the intermediate substrate 30, and thelid-substrate 50 which are made of a polyimide resin, respectively, andthe condenser substrate 20 and the evaporator substrate 40 which aremade of a metal having a high thermal conductivity, and are incorporatedinto the holes 31 and 32 of the intermediate substrate 30, respectively.

[0072] According to the above-described constitution, the evaporatorsubstrate 40 having the grooves of the wick is made of a metal or amaterial having such a high thermal conductivity as that of the metal,so that heat from a heat source can be transferred to the grooves of thewick at high efficiency. On the other hand, the flow-path substrate 10,the intermediate substrate 30, the lid-substrate 59, and so forth, madeof a polyimide resin, have a low thermal conductivity. Thus, the heatstored in the wick is less diff-used, i.e., the heat is enclosed. Thus,the quantity of the latent heat can be substantially increased, so thatthe cooling performance of the heat pipe can be enhanced. Moreover, thepolyimide resin is thermally stable and also is flexible. Thus, theresin is superior in strength, so that the service life of the coolingdevice 1 can be increased.

[0073] (Method of Producing Cooling Device)

[0074]FIG. 6 illustrates processes of producing the cooling device.

[0075] First, the open grooves 11 are formed in the flow-path substrate10, and the holes are formed in the intermediate substrate 30. Thegrooves and the holes function as a heat pipe (step 601). The opengroove 11 is formed at the surface 10 a of the flow-path substrate 10made of a polyimide resin. The open groove 11 functions as the liquidphase path 12, the gas phase path 15, the reservoir 13, the evaporationportion 14, and the low temperature portion 16. The holes 31 and 32 areformed in the intermediate substrate 30, which is made of a polyimideresin, so as to pass through the intermediate substrate 30.

[0076]FIGS. 7A to 7E show a process of forming the flow-path substrate10 as an example of the step 601.

[0077]FIG. 7A shows the flow-path substrate 10 before the processing,having a thickness of about 25 to 1000 μm.

[0078] Then, as shown in FIG. 7B, copper thin films 70 are formed onboth of the sides of the flow-path substrate 10 which are to be bondedto the intermediate substrate 30 and the lid-substrate 50, respectively.Regarding a method of forming the copper thin-films 70, both of thesides of the flow-path substrate 10 are processed with oxygen-plasma forsurface-modification of the substrate. Then, the copper thin films 70are formed thereon by vapor-deposition using sputtering so as to have athickness of about 50 nm to 1 μm.

[0079] Next, the formed flow-path substrate 10 having the copperthin-film 70 as shown in FIG. 7C is placed into a vacuum hot pressmachine, and heat at a temperature of 150° C. to 350° C. is applied tothe substrate under a reduced pressure of about 10⁻⁴ Torr to 10 Torr. Anadhesion layer 60 is fixed to the bonding surface of the lid-substrate50 at a pressure of 2 to 60 kg/cm² by hot-press bonding.

[0080] Next, as shown in FIG. 7D, the flow-path substrate 10 is set in alaser machine, and the third harmonic by YAG laser is irradiated theretofrom one side of the flow-path substrate 10 to work the substrate 10. Inthis case, it is necessary to input a desired pattern for the flow-pathsubstrate 10 into the laser machine in advance.

[0081] Then, as shown in FIG. 7E, the open groove 11 is formed in theflow-path substrate 10 so as to be passed trough the substrate 10 in thedesired pattern by means of the third harmonic by the laser.

[0082] The method of forming the open groove 11 in the flow-pathsubstrate 10 is described above. Regarding the intermediate substrate30, the copper thin-film and the adhesion layer 60 are formed in thesame manner as described above, and then, holes are formed bylaser-machining in the same manner as described above. Moreover,regarding the lid-substrate 50, the copper thin-film 70 is formed on thebonding surface thereof for the flow-path substrate 10. For thelid-substrate 50, it is not required to form holes. Thus, lasermachining is not carried out.

[0083] Next, grooves are formed on the condenser substrate 20 and theevaporator substrate 40 so that the function of the heat pipe can berealized (step 602).

[0084] First, as shown in FIG. 8A, a resist layer 81, e.g., made of SU8, which is an organic material, is formed on a plate 82. A resist layer83 is formed thereon in a pattern. The plate 82 and the layers 81 and 83constitute a pattern substrate 80.

[0085] Thereafter, as shown in FIG. 8B, UV rays are irradiated from theupper side of the pattern layer 80 so that the resist layer 81 isetched.

[0086] Next, as shown in FIG. 8C, the resist layer 83 is peeled off fromthe pattern substrate 80. A copper layer 84 is formed on the formedsurface by electro-forming of copper.

[0087] Then, the copper layer 84 is peeled off from the patternsubstrate 80 as shown in FIG. 8D. The formed copper layer 84 constituteseach of the condenser substrate 20 and the evaporator substrate 40 eachhaving grooves.

[0088] In the next process of the production of the cooling device, theflow-path substrate 10 and the lid-substrate 50 are joined to each otherby hot press joining (step 603).

[0089] As described above, the flow-path substrate 10 and thelid-substrate 50 are joined to each other via the copper thin-films andthe adhesion layer 60, which are formed on the bonding surfaces thereof,by applying a pressure of 2 to 60 kg/cm² under a reduced pressure of10⁻⁴ Torr to 10 Torr, at a temperature of 150 to 350° C., and for 5 to15 minutes.

[0090] After the flow-path substrate 10 and the lid-substrate 50 arejoined to each other, a thin film of DLC (not shown) is formed on thesurface of the produced flow-path for a working fluid (step 604).

[0091] In particular, first, a copper thin film is embedded into thesurface of the groove as the working fluid flow-path, which is formed inthe step 603, and is introduced into a PBII apparatus. Oxygen ions areimplanted into the surface of the groove to modify the copper surface.The portion not to be processed of the working fluid flow-path, i.e.,the portion excluding the groove, is protected by a metal mask or aresist mask as a protecting film. The flow-path substrate 10 and thelid-substrate 50 are placed in the center of the vacuum apparatus andare connected to a pulse electric source via an insulator. The vacuumapparatus is evacuated by means of a vacuuming pump. Moreover, oxygen,methane, nitrogen, titanium, or the like is converted to the pulseplasma at an ion source to be supplied synchronously with the pulse. Asdescribed above, the portion not to be processed is protected by theprotecting film. Accordingly, the DLC thin film can be formed in theregion to be selectively processed, i.e., the groove of the workingfluid flow-path only. Methane gas supplied from the ion source isconverted to its pulse-plasma. Thus, the DLC thin film with a thicknessof 3 μm is formed on the modified surface of the groove of the workingfluid flow-path. The contact angle of water to the surface is 70degrees. Moreover, CF₄ gas supplied from the ion source is converted toits pulse-plasma, and is ion-implanted for about 3 minutes, so thatfluorine is substituted for the hydrogen at the surface. In this case,the contact angle of water to the surface becomes 110 degrees. Thus, theDLC thin film is formed on the groove for the working fluid flow-path.The oxidation of the copper is described above. In the case in whichtitanium is used instead of copper and is implanted, similar results arealso obtained.

[0092] As shown in FIG. 10, the condenser substrate 20 and theevaporator substrate 40 are joined to the holes 31 and 32 of theintermediate substrate 30, respectively (step 605).

[0093] In particular, the condenser substrate 20 and the evaporatorsubstrate 40 are incorporated into the intermediate substrate 30 havingthe adhesion layer 60 made of a thermoplastic polyimide resin formed onthe bonding surface, from the bonding surface side of the substrate 30,and are joined thereto by application of a pressure of 2 to 60 kg/cm² ata predetermined temperature of 150 to 350° C. for 5 to 150 minutes underthe reduced pressure condition of 10⁻⁴ to 10 Torr.

[0094] Finally, as shown in FIG. 11, the flow-path substrate 10 to whichthe lid-substrate 50 is joined is joined to the intermediate substrate30 to which the condenser substrate 20 and the evaporator substrate 40are joined as described above (step 606).

[0095] In particular, the intermediate substrate 30 having the copperthin film and the adhesion layer 60 made of a thermoplastic polyimideresin formed on the bonding surface thereof is joined to the flow-pathsubstrate 10 by pressing at a pressure of 2 to 60 kg/cm² at atemperature of 150 to 350° C. for 5 to 15 minutes under the reducedpressure of 10⁻⁴ to 10 Torr.

[0096] In this embodiment, as the material for the condenser substrate20 and the evaporator substrate 40, copper is used. Other materials suchas silicon, nickel, or the like may be used.

[0097] In this embodiment, for the adhesion layer 60, a thermoplasticpolyimide resin is used. A thermosetting polyimide resin may be used. Inthe case, the thermosetting polyimide resin is cured by heating. Thus,suitably, the adhesion layer 60 is heated in the final stage of thejoining.

[0098] Moreover, according to this embodiment, laser processing isemployed for forming of the open groove 11 in the flow-path substrate 10and the holes 31 and 32 in the intermediate substrate 30. These grooveand holes may be formed by forming using a mold, i.e., by hot embossingor the like. In this case, the open groove 11, which is formed in theflow-path substrate 10 so as to be passed through the substrate 10 asdescribed above, are not limited to the open groove, and may be formedas an ordinary groove. In the case in which the groove 11 is formed asan ordinary groove, the lid-substrate 50 and the adhesion layer 60become unnecessary. Thus, the device can be reduced in thickness. Also,preferably, the DLC thin film is formed on the groove which constitutesthe flow-path of the heat pipe.

[0099] Referring to the processing of the open groove 11 of theflow-path substrate 10 and the holes 31 and 32 of the intermediatesubstrate 30, etching (chemical etching using an alkali solution ofhydrazine, KOH, or the like, or plasma-etching using oxygen plasma),sand-blasting, and so forth may be employed.

[0100] According to this embodiment, for formation of the condensersubstrate 20 and the evaporator substrate 40, a UV-LIGA method is used.The formation may be carried out by photo-etching, machining, reactiveion etching (RIE) or the like.

[0101] The heat pipe can be efficiently produced according to theabove-described production methods.

[0102] (Other Example of Cooling Device)

[0103]FIG. 12 shows a flexible cooling device 120 in which a condensermember 122 and an evaporator member 124 are connected to each other viaa flexible substrate 121.

[0104] The condenser member 122 and the evaporator member 124 are madeof a polyimide resin, respectively. The condenser substrate 20 and theevaporator substrate 40 are incorporated therein by the above-describedmethod.

[0105] The flexible substrate 121 is made of a plastic, and contains theflow-path 123 of a heat pipe. These members and the substrates areintegrated to form the heat pipe.

[0106] The flexible substrate 121 can be desirably deformed. Forexample, the evaporator member 124 fixed, e.g., to a heating unit of anelectronic apparatus, and the flexible substrate can be disposed so asto be extended in close contact with the surface features of theelectronic apparatus.

[0107] According to the above-described structure of the cooling device,the heat pipe can be efficiently installed even in a narrow space. Thus,the size or thickness of the electronic apparatus or the like can bereduced.

[0108] (Electronic Apparatus)

[0109]FIG. 13 is a schematic perspective view of a personal computer inwhich the cooling device of the present invention is mounted.

[0110] A personal computer 130 contains a slot 131 to or from which astorage medium 134 having a flash memory 133 and a driver 132 isattached or detached, and a central processing unit (CPU) 135. Thecooling device 1 of the present invention is arranged in the personalcomputer 130 so that the wick is positioned, e.g., under the driver 132of the storage medium 134 which is disposed in the slot 131.

[0111] Also, the cooling device 1 of the present invention may bearranged so that the evaporator is positioned adjacently to the centralprocessing unit 135. In this case, the condenser is suitably positionedadjacently to a cooling fan or the like (not shown). Thereby, heatgenerated from the central processing unit 135 is absorbed by theevaporator. The heat is released from the condenser due to the action ofthe cooling fan. Thus, the central processing unit 135 can be cooled.

[0112] In the above-description, the personal computer is referred to asan example of the electronic apparatus. The cooling device of thepresent invention may be mounted onto other electronic apparatus such asa digital camera, a video camera, or the like.

[0113] (Display Unit)

[0114]FIG. 14 is a schematic perspective view of a liquid crystaldisplay unit onto which the cooling device of the present invention ismounted.

[0115] A liquid crystal display unit 140 contains a driver 141, adisplay section 142, and a cooling fan 143. The cooling device 1 of thepresent invention is arranged in the liquid crystal display unit so thatthe evaporator is positioned adjacently to the driver 141, and thecondenser is positioned adjacently to the cooling fan 143. The heatgenerated from the driver 142, caused by the operation of the liquidcrystal display unit 140, is absorbed by the evaporator. The absorptionheat causes the liquid in the cooling device 1 to be evaporated andflows into the condenser via the flow-path. The cooling fan 143 coolsthe condenser so that the heat of the gas flown into the condenser isreleased, and the gas is liquefied again. The liquid, produced in thecondenser, is flown into the evaporator via the flow-path, and absorbsthe heat generated from the driver 141 to be evaporated again. Thedriver 141 can be cooled by the above-described circulation of theliquid in the cooling device 1. Similarly, the display section 142 canbe cooled by disposing the evaporator adjacently to the display section142.

What is claimed is:
 1. A cooling device comprising: a first memberhaving at least a wick as a component of a heat pipe; a second memberphysically separated from the first member and provided with a condenseras a component of the heat pipe; and a flexible substrate interposedbetween the first member and the second member and having a flow-pathformed therein so as to connect the wick and the condenser to eachother, wherein at least one of the first member and the second memberbeing made of a polyimide resin.
 2. A cooling device according to claim1, wherein the first member and the second member having grooves made ofat least one of a metal and a material having a thermal conductivitysubstantially equal to that of a metal.
 3. A cooling device according toclaim 1, wherein the flow-path formed in the flexible substrate has adiamond-like carbon film formed therein.